An allograft or allogeneic transplant or homograft is a transplant in which transplanted cells, tissues, or organs are sourced from a genetically non-identical member of the same species. Most human tissue and organ transplants are allografts.

In contrast, a transplant from another species is called a xenograft. A transplanted organ or tissue from a genetically identical donor, i.e., an identical twin, is termed an isograft. Finally, when a tissue is transplanted from one site to another on the same patient, it is termed an autograft.

When a host mounts an immune response against an allograft or xenograft, the process is termed rejection.

A variety of tissue and organs types can be used for allografts. These include: